The entire disclosure of commonly assigned U.S. Pat. No. 5,383,312 is hereby incorporated by reference herein.
The present invention relates in general to shields used to prevent air-borne particles from contaminating the environment within the shield. More particularly, the invention relates to clean environment enclosures typically employed in paint operations in manufacturing plants.
In manufacturing facilities where products are painted, it is necessary that the environment immediately surrounding the paint operation be as free as possible from dust, dirt and other air-borne contaminants in order to provide the best application of paint to the product.
Various forms of enclosures have been used to prevent air-borne contaminants from interfering with the paint application process. Such contaminant shields or "clean environment enclosures" are typically provided with positive airflow into the enclosure to prevent dust and dirt from entering the open ends of the enclosure. They are built of rigid side and top panels with opposed ends, with an attached flexible sheet(s) covering the periphery.
Two examples of prior art contaminant shields are disclosed in U.S. Pat. Nos. 4,769,962 and 4,860,778. These enclosures are relatively expensive to manufacture and require lengthy installation times. For example, with each of these prior art shields flexible sheets are attached to individual panels in a relatively complicated manner, using multiple connectors and/or a "tongue-in-groove" connection system, with clamps or other supports also being employed.
The shield disclosed in U.S. Pat. No. 5,383,312 is an improvement over these prior art shields, and provides a controlled environment enclosure which can be more easily and inexpensively constructed, quickly altered in structure, adapted for different applications and easily repaired. Further improvements in contaminant shields are possible, however.
Most contaminant shields used for automotive painting utilize Unistrut (steel) frame members and custom plastic Unistrut caps to retain the plastic film. The Unistrut frame members consist of open section (C-channel) lengths which are only available in steel, and which do not provide adequate strength if they are constructed of lighter weight materials such as aluminum. in another design, a frame is constructed of tubular steel, a steel rod is welded to the front face of the frame around its perimeter, and a plastic clip is used to retain the plastic to the steel frame.
In still another design, a plastic extrusion is inserted into an open section C-channel, the film is inserted over the extrusion, and a plastic bead is then inserted over the film to couple with the extrusion and seal the film. This design is overly complicated and also provides less strength since it employs an open section frame assembly.
In a further design disclosed in U.S. Pat. No. 5,181,354, a main frame of tube steel has a steel rod welded to its surface. A rounded retainer or clip is snapped over the rod, securing a shrink film in place. One disadvantage with this design is that the convex shape of the retainer creates a dust ledge. A second disadvantage is that the film tends to pool with water adjacent the raised retainer surface.
In every known design, the frames are constructed of steel. However, steel frames are heavy and unwieldy. It is also difficult to fasten modular steel panels, which are typically shipped to a job site for installation, using conventional means such as self-drilling ("Tek") screws.
An object, therefore, of the present invention is to provide an contaminant shield which can be economically constructed from inexpensive materials.
Another object of the present invention is to provide a lightweight contaminant shield which can be quickly and easily constructed in the field.
A further object of the present invention is to provide a contaminant shield which can be assembled into a variety of shapes without providing a dust ledge, and which can be easily altered or repaired.